Unit 4

This section discusses subroutines (more correctly, methods) in the context of viewing them as “black boxes” that perform actions based on inputs. In this view, the mechanism or inner workings of the method is not as important as the function it provides.

This section provides background to subsequent sections. Read and review it carefully.

This section discusses the role of the subroutine (correct term is method) in Java, as well as the static subroutine and static variables, which are consequences of the way Java has been designed. The section also discusses how to call a subroutine (method) and how subroutines (methods) can be used in programs. Finally, member variables are introduced and discussed.

Read and review this section carefully.

• 4.2.1 Subroutine Definitions
• 4.2.2 Calling Subroutines
• 4.2.3 Subroutines in Programs
• 4.2.4 Member Variables

This section discusses how to send information into a method using parameters. The concept of overloading as it pertains to subroutines (methods) is covered, followed by an example. Parameters using arrays and command-line arguments are discussed next. The section covers throwing exceptions in subroutines (methods) and ends with a discussion of global and local variables.

Read and review this section carefully.

• 4.3.1 Using Parameters
• 4.3.2 Formal and Actual Parameters
• 4.3.3 Overloading
• 4.3.4 Subroutine Examples
• 4.3.5 Array Parameters
• 4.3.6 Command-line Arguments
• 4.3.7 Throwing Exceptions
• 4.3.8 Global and Local Variables

This section covers the retrieval of output from a method using the return statement. Some examples are explored and, finally, the 3N+1 problem is revisited.

Read and review this section carefully.

• 4.4.1 The return statement
• 4.4.2 Function Examples
• 4.4.3 3N+1 Revisited

This section is an introduction to lambda functions. These are fairly new to Java, introduced in Java 8. Lambda functions offer some very nice programming features, but keep in mind that this topic is more suited to advanced programming courses. Lambda functions are beyond the scope of this course.

• 4.5.1 First-class Functions
• 4.5.2 Functional Interfaces
• 4.5.3 Lambda Expressions
• 4.5.4 Method References

This section covers some important topics in the course. First, the notion of an Application Programming Interface (API) is discussed as a type of toolbox that you can use in your programs. From there, the Java standard packages are introduced and discussed, followed by an explanation of how to use these standard packages in your own programs. The section ends with a discussion of the Java code documentation package, Javadoc, and closes by mentioning static import.

Read and review sections 4.6.1 through 4.6.5 carefully. Section 4.6.6 is beyond the scope of this course.

• 4.6.1 Toolboxes
• 4.6.2 Java’s Standard Packages
• 4.6.3 Using Classes from Packages
• 4.6.4 About Modules
• 4.6.5 Javadoc
• 4.6.6 Static Import

This section covers the important topic of program design, and includes a discussion of pre- and postconditions with respect to subroutine (method) design. The next two sections discuss an example of graphical user interface (GUI), resulting in a final program that is beyond the scope of this course.

Read and review section 4.7.1 carefully. Sections 4.7.2 and 4.7.3 are beyond the scope of this course.

• 4.7.1 Preconditions and Postconditions
• 4.7.2 A Design Example
• 4.7.3 The Program

This section covers some essential information regarding declaration and initialization of variables in Java programs. Also covered are named constants and a discussion of a variable’s scope—that is, where a variable can be seen and used in a program.

Read and review this section carefully.

• 4.8.1 Initialization in Declarations
• 4.8.2 Declaring Variables with var
• 4.8.3 Named Constants
• 4.8.4 Naming and Scope Rules

It is a good practice to attempt the programming exercises in the textbook, to put the topics you have learned into concrete Java code. This, in turn, allows you to reflect on the material you have read. Skip any exercises relating to topics in Chapter 4 that are not covered in the course.

It is a good practice to review the chapter quizzes in the textbook, as the questions allow you to reflect on the material you have read.